This invention relates to acyclic machines employing liquid metal electrical current collectors, and more particularly to apparatus for maintaining liquid metal in contact with limited surface areas at all angular velocities including zero.
In an acyclic machine using, instead of solid brushes, liquid metal current collectors on a collector ring, the liquid metal forms a portion of the current carrying loop. Due to the relative rotation of the collector rings, positive containment of the liquid metal employed in the place of solid brushes, which define clearly identified contact areas, has required use of rigid containment walls machined to exceptionally close tolerances and biased toward the rotor collector ring.
In generator applications as shown, for example in L. M. Harvey U.S. Pat. Nos. 3,211,936, and 3,546,508 issued Oct. 12, 1965 and Dec. 8, 1970, respectively, both of which are assigned to the instant assignee, centrifugal force generated within the liquid as it is caused to rotate by the relatively rotating collector rings has been successfully used to retain liquid metal in the collector site at speeds above a minimum rotor angular velocity. In these prior generators, if rotor angular velocity were to fall below a minimum value, or completely stop, the liquid metal would drain from its location in the collector gap. Therefore, the generator would normally not be operated at less than about 25% of its rated speed, nor at any speed in a reverse direction.
In motor applications, such as ship propulsion, capability of applying full torque (and overload torques) at any and all motor speeds (e.g., up to 1500 RPM) in both directions of rotation, including zero speed and emergency reversals, is essential. At zero and low rotor angular velocities, centrifugal force is either completely unavailable or insufficient to retain the liquid metal in the collector site. However, if the liquid metal is not retained in the collector site, either the electric circuit will be broken or electrical arc-over will occur. In either case, the motor will be rendered inoperative. To overcome these problems, the method and apparatus described and claimed in B. D. Hatch U.S. Pat. No. 3,989,968, issued Nov. 2, 1976 and J. D. Hurley U.S. Pat. No. 4,027,184, issued May 31, 1977, both of which patents are assigned to the instant assignee, have been devised. The invention in each of these patents is intended to prevent or counteract Lorentz expulsion forces on liquid metal in the current collectors of acyclic machines. In each of these patents, the contact between rotor and stator collector rings involves passage of electrical current through an intermediate metallic portion. Consequently, current passing between rotor and stator collector rings must flow through two, circumferentially-separated volumes of liquid metal and four liquid metal-to-solid metal interfaces. As a result, collector electrical resistance, and therefore loss, is larger than it would be if only a single volume of liquid metal were interposed between the rotor and stator collector rings. In addition, the large amount of total wetted area results in viscous losses which could be reduced by reducing the total wetted area.
Patent application Ser. No. 934,100, filed Aug. 16, 1978 by R. A. Marshall and assigned to the instant assignee provides a single layer liquid metal contact between relatively-moving rotor and stator collector rings. This application involves use of rigid walled enclosures biased toward the rotor collector ring to contain a volume of liquid metal in contact with each of the collector rings. In application Ser. No. 838,714, filed Oct. 3, 1977, now U.S. Pat. No. 4,146,807, issued Mar. 27, 1979, by the instant inventor and assigned to the instant assignee and incorporated herein by reference, a plurality of circumferentially-abutting enclosures are located around the circumference of the collector rings to form a plurality of confined contact areas for the liquid metal current collectors. By frictionally-engaging the ends of the adjacent enclosures, a flexible arch arrangement is provided which allows for slight eccentricity of the relatively-rotating collector rings. Use of rigidly-formed containment enclosures requires that the parts be machined to close tolerances and biased toward the rotor collector ring by springs or other devices located between the fixed collector ring and the containment wall. This adds a requirement for highly skilled machinists to manufacture the containment walls, and adds assembly steps in mounting the containment walls on springs within the machine, and requires that some device be used to hold the containment wall securely until the rotor is positioned within the machine.
Accordingly, one object of the instant invention is to provide a liquid metal current collector which allows continuous electrical contact between predetermined areas of an acyclic machine stator collector ring and rotor collector ring thereof.
Another object is to provide a liquid metal electrical current collector between the rotor and stator collector rings in an acyclic machine having a construction such that the containment wall is permanently affixed to one of the current collector rings, while providing a resilient containment wall to accommodate variations in the surface of the other collector ring.